The invention relates to, in general, a process for manufacturing composite components or parts and, in particular, a resin infusion system for the manufacture of parts having generally hollow cross-sections.
Polymer matrix composites (PMC) may be used in a variety of applications, such as in the aerospace industry, due to their favorable combination of mechanical properties. In general, PMCs can be used in structures that are lighter or stronger than their metallic counterparts. PMCs typically consist of a reinforcing fiber/fabric, such as fiberglass, Kevlar®, or carbon, embedded in a polymer matrix, such as a thermoset or thermoplastic polymer, that binds together the fiber/fabric. There are numerous manufacturing processes for PMCs. One family of processes is resin transfer molding (RTM). In RTM dry fiber/fabric is laid up onto on open or inside a closed mold and formed to the shape of the part. Then liquid resin is infused into the dry fiber/fabric, ideally completely wetting all the fibers and encapsulating them in the resin. Finally, the resin is cured, in the case of a thermoset polymer matrix, or cooled, in the case of thermoplastic polymer matrix, to solidify the composite structure and form the part.
In an RTM process, great care and planning is typically required to ensure that the resin flows in the desired way around the dry fiber/fabric, and completely wets the fibers. The resin can be pushed under pressure into the fiber/fabric, or pulled under a vacuum, or a combination of each. The viscosity of the resin can be controlled or affected to aid in resin flow and wetting. Flow channels can be provided in the part or through the use of consumables in order to allow the liquid resin to flow around and cover the surface of the fiber/fabric, before turning and flowing through it.
Another major family of manufacturing processes utilizes prepregs. Prepregs are reinforcing fibers or fabrics that are pre-impregnated with a polymer matrix. The prepreg is flexible when molded into the part shape, then cured or hardened to a rigid form. One form or prepreg processing has been developed for forming parts that are complex in shape, and have a generally hollow or open cross-sectional shape. The process involves the use of polymer mandrel that is formed into the interior cross-sectional shape of the part. Then the prepreg fabric is laid up on or around the mandrel to form a preform. The mandrel and the preform are placed inside of a closed, sealed mold. Provision is made in the mold tooling to allow hot, compressed air to be injected inside of the mandrel. The mandrel heats up and becomes flexible, and the pressure of the air pushes the mandrel against the preform and against the external mold surface of the mold tooling. Through the application of pressure and heat against the preform, the preform is consolidated and then cured. The cured part, with the mandrel still inside, is removed from the mold tooling. The mandrel can then be reheated to a temperature which makes it pliable enough to remove from the part interior.
The above-described process of forming complexly shaped, hollow cross-section parts is effective when the PMC material system to be used for the part is available in prepreg form. However, some material systems are not available or well-suited to the prepreg form, or may be too expensive or unwieldy in prepreg form. It would be beneficial to be able to use the above-described process with dry fiber/fabric and infuse the resin.